The present invention relates to implantable neural stimulators, such as a cochlear implant, and more particularly to an implantable neural stimulator wherein the bandwidth necessary for forward telemetry is reduced through the use of spatial decimation.
While the present invention relates to implantable neural stimulators, it will be described by way of example with reference to a cochlear implant, which represents one type of implantable neural stimulator. The principles of the present invention may be readily applied by those of skill in the art to all types of implantable neural stimulators. Hence, the invention is not limited to a cochlear implant.
Electrical stimulation of predetermined locations within the cochlea of the human ear through an intra-cochlear electrode array is described, e.g., in U.S. Pat. No. 4,400,590. The electrode array shown in the '590 patent comprises a plurality of exposed electrode pairs spaced along and imbedded in a resilient curved base for implantation in accordance with a method of surgical implantation, e.g., as described in U.S. Pat. No. 3,751,615. The system described in the '590 patent receives audio signals, i.e., sound waves, at a signal processor (or speech processor) located outside the body of a hearing impaired patient. The speech processor converts the received audio signals into modulated RF data signals that are transmitted by a cable connection through the patient's skin to an implanted multi-channel intracochlear electrode array. The modulated RF signals are demodulated into analog signals and are applied to selected ones of the plurality of exposed electrode pairs in the intra-cochlear electrode so as to electrically stimulate predetermined locations of the auditory nerve within the cochlea.
U.S. Pat. No. 5,938,691, incorporated herein by reference, shows an improved multi-channel cochlear stimulation system employing an implanted cochlear stimulator (ICS) and an externally wearable speech processor (SP). The speech processor employs a headpiece that is placed adjacent to the ear of the patient, which receives audio signals and transmits the audio signals back to the speech processor. The speech processor receives and processes the audio signals and generates data indicative of the audio signals for transcutaneous transmission to the implantable cochlear stimulator. The implantable cochlear stimulator receives the transmission from the speech processor and applies stimulation signals to a plurality of cochlea stimulating channels, each having a pair of electrodes in an electrode array associated therewith. Each of the cochlea stimulating channels uses a capacitor to couple the electrodes of the electrode array.
Other improved features of a cochlear implant system are taught, e.g., in U.S. Pat. Nos. 5,626,629; 6,067,474; 6,157,861; 6,219,580; 6,249,704; and 6,289,247, each of which patents is incorporated herein by reference. Further enhancements are disclosed, e.g., in pending and co-owned U.S. patent application Ser. No. 10/218,645, filed Aug. 13, 2002, and U.S. patent application Ser. No. 10/218,616, filed Aug. 13, 2002, each of which patent applications is also incorporated herein by reference.
The implantable cochlear stimulators described in the '629, '474, '861 and '580 patents are also able to selectively control the pulse width of stimulating pulses that are applied through the electrode array to the cochlea, and the frequency at which the stimulating pulses are applied.
The new generation of cochlear implants that have the enhanced processing power, and which can provide multiple platforms for delivering electrical stimuli to the auditory nerve, including high frequency pulsitile stimulation having current pulses of controlled amplitude, width and frequency, are frequently referred to as a “bionic ear” implant.
The bionic ear, or equivalent, cochlear implants offer operating modes that provide very high-speed stimulation designed to increase temporal fine structure while also activating the stochastic resonance mode. The stochastic resonance mode has heretofore typically been lost to patients whose hearing loss qualifies them to receive a cochlear implant. The high rate stimulation mode advantageously has been found to provide performance benefits in, e.g., CNC word testing under quiet conditions, and also provides significant improvements in word testing in noisy conditions. Additionally, it has been estimated that the high rate stimulation mode will increase hearing fidelity to the point where significant improvements are achieved relative to the sound of music and other broadband acoustic signals. Thus, it is seen that the high rate stimulation mode represents a highly sought-after mode for inclusion in a cochlear implant. Similar stochastic resonance and other benefits are achievable with any neural implant device that utilizes high rate electrical stimulation parameters. See, e.g., PCT Publication No. WO 03/015863 A2, published 27 Feb. 2003, based on PCT International Patent Application Serial No. PCT/US02/25861, filed 13 Aug. 2002, incorporated herein by reference.
One problem resulting from the use of very fast stimulation rates with narrow biphasic pulses is that the system power requirements increase significantly. While the potential improvements in sound quality (or other neural performance) can be significant, these high rate modes can cause serious reduction in battery operating times. Hence, it is seen that there is a need for an operating mode that provides the benefits of high-speed stimulation, but which could be operated at significantly lower power levels.